In the rotary cutting rule field, particularly the manufacturing end, various approaches are employed to "work" the raw material in order to facilitate its formation.
For example, U.S. Pat. No. 3,645,155 describes a method for making a form member for a cutting machine comprising forming notches or openings in a rule spaced from the operative edge, and applying a ductile metal base.
Also, applicant's rule as described in U.S. Pat. No. 4,351,210, embodies a notched inner edge with a keyhole shape. A relevant article appeared in the December 1969 edition of Diemaking, Diecutting and Converting, entitled "Steel Rule for Rotary Die-Cutting of Corrugated Containers", authored by David K. Hart. The article identifies the need to notch the rule along its bottom edge for a distance something over half of its height in order to facilitate curving the rule.
Applicant's assignee and its predecessor in business have been in the rule manufacturing business for over fifty years. In their experience, curved rules, practically speaking, have been notched for the purpose stated above.
In notching and bending or curving rules, such as the one in U.S. Pat. No. 4,351,210, it has been the assignee.varies.s observation that a slight bulging of the material, or tit, appears at the top of the keyhole or other notch. When the rule is inserted into the wooden dieboard, the contact surface area between the rule and die as a result are minimized. The retention capability of the die is thus reduced necessitating frequent resetting or replacement of the rule.
Also, the notching method results in the following relative disadvantages:
extra time and work to fabricate the finished product; PA1 tendency of the resultant product to not bend accurately; PA1 the requirement for stress relief of the metal; other distortions and excess stress in the metal; hysteresis effects in the formed steel allowing it to tend to revert back toward its original form; weakening and fatiguing of the metal leading to possible breakage.
It is, therefore, a primary object of this invention to provide a new method for manufacturing curved metal or other materials in a way that obviates any one or all of the above disadvantages and in a less costly manner.